Low temperature molten salt synthesis of SrTiO3 submicron crystallites and nanocrystals in the eutectic NaCl-KCl

An eutectic NaCl-KCl molten salts method has been developed for the synthesis of SrTiO₃ submicron crystallites and nanocrystals from SrO₂ and two kinds (submicron and nano-sized) of TiO₂ powders at 700 °C, which was much lower than that (generally > 1000 °C) of the conventional solid state reactions. The characterization results from X-ray diffraction and X-ray photoelectron spectroscopy revealed that the obtained products were pure perovskite phase SrTiO₃ without any contamination of Na, K, and Cl ions. The scanning electronic microscopy and transmission electron microscopy images disclosed that the starting TiO₂ played an important role in the morphology and size of the obtained SrTiO₃: while the product derived from TiO₂ submicron crystallites comprised faceted submicron crystallites of about 95-184 nm, that derived from TiO₂ nanocrystals comprised quadrate nanocrystals of about 20-61 nm. Besides, based on the experiments without the molten NaCl-KCl eutectic, at different temperatures and times, and using different kinds of TiO₂, the possible formation mechanism of SrTiO₃ submicron crystallites and nanocrystals was proposed.     

Syntheses of Mn3O4 and LiMn2O4 nanoparticles by a simple sonochemical method

Mn₃O₄ and LiMn₂O₄ nanoparticles were prepared by a simple sonochemical method which is environmentally benign. First, Mn₃O₄ nanoparticles were prepared by reacting MnCl₂ and NaOH in water at room temperature through a sonochemical method, operated at 20 kHz and 220 W for 20 min. Second, LiOH was coated onto the resulting Mn₃O₄ under the same sonochemical conditions as above. The thickness of coated LiOH on Mn₃O₄ obtained from the reaction ratio of 3:1 between LiOH and Mn₃O₄ was about 4.5–5.5 nm range. Then, by heating those LiOH-coated Mn₃O₄ particles at the relatively low temperature of 300–500 °C for 1 h, they were transformed into phase-pure LiMn₂O₄ nanoparticles of about 50 to 70 nm size in diameter.     

Synthesis and characterization of nanocrystalline manganese pyrophosphate Mn2P2O7

Mn₂P₂O₇ polyhedral particles were synthesized by simple and cost-effective method using manganese nitrate hydrate and phosphoric acid in the presence of nitric acid with further calcinations at the temperature of 800 °C. The crystallite size obtained from X-ray line broadening is 31 ± 13 nm for the Mn₂P₂O₇. The X-ray diffraction and SEM results indicated that the synthesized nanoparticles have only the structure without the presence of any other phase impurities. The FT-IR and FT-Raman spectra show characteristic bands of the P₂O₇⁴⁻ anion. The UV–Vis–NIR spectrum confirms the octahedral coordination of Mn²⁺ ion.     

Preparation of SrAl2O4: Eu, Dy nanometer phosphors by detonation method

SrAl₂O₄: Eu²⁺, Dy³⁺ nanometer phosphors were synthesized by detonation method. The particle morphology and optical properties of detonation soot that was heated at different temperatures (600–1100 °C) had been studied systematically by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Results indicated SrAl₂O₄: Eu²⁺, Dy³⁺ nanometer powders in monoclinic system (a = 8.442, b = 8.822, c = 5.160, β = 93.415) can be synthesized by detonation method, when detonation soot was heated at 600–800 °C. The particle size of SrAl₂O₄: Eu²⁺, Dy³⁺ is 35 ± 15 nm. Compared with the solid-state reaction and sol-gel method, synthesis temperature of the detonation method is lower about 500 and 200 °C respectively. After being excited under UN lights, detonation soot and that heated at 600–1100 °C can emit a green light.     

Formation of SrTiO3 from Sr-oxalate and TiO2

SrTiO₃ powder has been prepared from Sr-oxalate and TiO₂ precursors, instead of using titanyl-oxalate. Sr-oxalate was precipitated from nitrate solution onto the surface of suspended TiO₂ powders. Crystallization of SrTiO₃ from the precursor was investigated by TGA, DTA and XRD analysis. It is evident that precursor, upon heating, dehydrates in two stages, may be due to the presence of two different types of Sr-oxalate hydrates. Dehydrated precursor then decomposes into SrCO₃ and TiO₂ mixture. Decomposition of SrCO₃ and simultaneous SrTiO₃ formation occur at much lower temperature, from 800 °C onwards, due to the fine particle size of the SrCO₃ and presence of acidic TiO₂ in the mixture. The precursor completely transforms into SrTiO₃ at 1100 °C. About 90 nm size SrTiO₃ crystallites are produced at 1100 °C/1 h, due to the lower calcination temperature and better homogeneity of the precursor.     

Photosensitivity in GeO2–SiO2 glasses and optical waveguides

Permanent refractive index changes caused by a KrF excimer laser operating at 248 nm in GeO₂–SiO₂ glasses deposited on Si (100) substrates using flame hydrolysis deposition (FHD) are presented. The sample was amorphouslike investigated by X-ray diffraction (XRD), and the ratio of Ge:Si is 14:86 from X-ray photoelectron spectroscopy (XPS) analysis. The 10-min irradiation with a KrF excimer laser (10 Hz, 187 mJ/cm²) induced a positive refractive index change of 0.341% at 1550 nm, which has achieved an international level of this field. An innovative photomask with a Cr-loaded structure coated on a UV quartz glass, was used to fabricate a 50 μm gap with a period of 100 μm waveguide grating under 1460 mJ/cm²/pulse at 6 Hz, and the diffraction patterns were observed clearly. The extinction coefficients of the samples are also measured over the range 250–1600 nm.     

Photo-induced formation of hydroxyapatite on TiO2 synthesized by a chemical–hydrothermal treatment

The formation of hydroxyapatite (HAp) on TiO₂ surfaces under continuous ultraviolet (UV) irradiation was investigated. Pure Ti substrates were chemically treated with H₂O₂/HNO₃ at 353 K for 20 min to form a TiO₂ gel layer. The specimens were then hydrothermally treated with an aqueous NH₃ solution in an autoclave at 453 K for 12 h. An adhesive and sufficiently crystallized anatase-type TiO₂ film could be synthesized on the Ti surface. The specimens were immersed in simulated body fluid in darkness or under UV irradiation with a centered wavelength of λ = 365 nm. Under dark conditions, a thin homogeneous HAp film was formed, with just a few spherical clusters of HAp. The UV illumination promoted the formation of HAp clusters, which may be due to the generation of functional Ti–OH or Ti–O groups on the TiO₂ surface. On the other hand, the UV light produced electron-hole pairs in the TiO₂, and the photogenerated holes that migrated to the surface repelled the Ca²⁺ ions in the solution. As a consequence, the UV irradiation suppressed the formation of a HAp thin film.     

Synthesis and characterization of NiAl2O4 nanoparticles obtained through gelatin

Nanoparticles of NiAl₂O₄ were synthesized by heating (500-1000 °C) the dried resin resultant of a mixture in aqueous solution of gelatin, NiCl₂·6H₂O and AlCl₃·6H₂O. The particle size and microstrain were calculated from the line broadening of X-ray powder diffraction peaks through the Rietveld method refinement: these are 3.9-16 nm and − 0.743-0.139%, respectively. The NiAl₂O₄ nanoparticles were characterized by X-ray powder diffraction (XRPD), thermo gravimetric analysis (TG), BET and TEM techniques.     

Synthesis of TiO2 sol in a neutral solution using TiCl4 as a precursor and H2O2 as an oxidizing agent

Nanosize TiO₂ thin film on glass substrate was obtained through dip-coating method using TiO₂ sol. Suspended nanosize TiO₂ sols with anatase structure in aqueous solution were synthesized by sol–gel method using TiCl₄ as a precursor. TiCl₄ was reacted with an aqueous solution of NH₄OH to form Ti(OH)₄, and H₂O₂ was then added to form peroxo titanic acid. It was further heated in water and converted to TiO₂. The effects of the preparation parameters, viz., pH value of the Ti(OH)₄ gel, concentration of H₂O₂, and heating temperature and time, on the properties of the TiO₂ sol were investigated. The materials were characterized by X-ray diffraction, Fourier transform-infrared spectroscopy, and transmission electron microscopy. The results showed that the primary TiO₂ particles were rhombus with the major axis ca. 10 nm and minor axis ca. 4 nm, and were in anatase structure. The sol was excellent in dispersibility and was stable in neutral and even slight basic conditions for at least 2 years without causing agglomeration. The best preparation condition was optimized with the pH value of Ti(OH)₄ gel at 8, H₂O₂/TiO₂ mole ratio of 2, and heating at 97 °C for 8 h. The transparent adherent TiO₂ film on glass substrates exhibits strong hydrophilicity after illuminating with ultraviolet light and it can be used as an efficient photocatalyst.     

Synthesis and luminescent properties of SrAl2O4:Eu green-emitting phosphor for white LEDs

SrAl₂O₄:Eu²⁺ phosphor was prepared by a solid-state reaction in CO-reductive atmosphere. X-ray powder diffraction (XRD) analysis confirmed the formation of SrAl₂O₄:Eu²⁺. Field-emission scanning electron-microscopy (FE-SEM) observation indicated that the microstructure of the phosphor consisted of irregular fine grains with an average size of about 7–8 μm. Photoluminescence measurements showed that the phosphor can be efficiently excited by UV–visible light from 350 to 430 nm, and exhibited bright green emission peaked at about 516 nm. Bright green LEDs were fabricated by incorporating the phosphor with an InGaN-based UV chip. All the characteristics indicated that SrAl₂O₄:Eu²⁺ is a good candidate phosphor applied in white LEDs.     

Synthesis of WO3 in nanoscale with the usage of sucrose ester microemulsion and CTAB micelle solution

WO₃ nanoparticles were successfully prepared using first the low temperature hydrolysis method and second the chemical reaction method in water-in-oil sucrose ester microemulsion consisting of S1570, 1-butanol, tetradecane and aqueous phase. In this study WO₃ nanoparticles also were prepared using the CTAB micelle solution. The resultant WO₃ nanoparticles have been investigated with X-ray diffraction (XRD), transmission electron microscopy (TEM), variable pressure scanning electron microscope (SEM) equipped with energy dispersive X-ray analysis (EDX) and X-ray photoelectron spectroscopy (XPS). The shape and particles size of the resultant WO₃ nanoparticles from both methods in sucrose ester microemulsion show similar spherical shape and size range between 10 and 50 nm. The WO₃ nanoparticles prepared with the CTAB micelle solution show spherical shape with the size range average of 25-50 nm.     

Influence of ZnO additions to 0.8(Mg0.95Co0.05)TiO3–0.2Ca0.6La0.8/3TiO3 ceramics on sintering behavior and microwave dielectric properties

The effects of ZnO addition on the microstructures and microwave dielectric properties of 0.8(Mg_0.95Co_0.05)TiO3–0.2Ca_0.6La_0.8/3TiO₃ ceramics were investigated. ZnO was selected as liquid phase sintering aids to lower the sintering temperature of 0.8(Mg_0.95Co_0.05)TiO3–0.2Ca_0.6La_0.8/3TiO₃ ceramics. With ZnO additives, the densification temperature of 0.8(Mg_0.95Co_0.05)TiO₃–0.2Ca_0.6La_0.8/3TiO₃ can be effectively reduced from 1450 to 1200–1325 °C. The crystalline phase exhibited no phase difference at low addition levels (0.25–2 wt.%). It is found that low-level doping of ZnO (0.25–2 wt.%) can significantly improve the density and dielectric properties of 0.8(Mg_0.95Co_0.05)TiO₃–0.2Ca_0.6La_0.8/3TiO₃ ceramics. The quality factors Q × f were strongly dependent upon the amount of additives. Q × f values of 36 000 and 13 000 GHz could be obtained at 1200–1325 °C with 1 and 2 wt.% ZnO additives, respectively. During all additives ranges, the relative dielectric constants were significantly different and ranged from 23.1 to 27.96. The temperature coefficient varies from 14.1–24.3 ppm/°C.     

Mechanochemical synthesis and characterization of TiB2 and VB2 nanopowders

A novel method for the synthesis of transition-metal boride nanopowder has been developed using a mechanochemical reaction between LiBH₄, LiH and transition-metal chloride (TiCl₃ and VCl₃) by high energy ball milling. This method successfully produces TiB₂ and VB₂ particles dispersed within a soluble LiCl matrix. Subsequent washing with distilled water, ethanol and acetone to remove the LiCl matrix phase yields TiB₂ and VB₂ nanopowders of 15-60 nm particle size. From the X-ray diffraction patterns and high resolution transmission electron microscopy image, it is found that each particle is polycrystalline consisting of 3-5 nm crystallites. Neither particle nor crystallite size are increased significantly after heating at 680 °C.     

Localized surface plasmon resonance sensing properties of photocatalytically prepared Au/TiO2 films

Photocatalytic deposition of Au nanoparticles from a mixed aqueous solution of HAuCl₄ and ethylene glycol onto TiO₂ films (Au/TiO₂ films) was carried out by using ultraviolet light irradiation at room temperature. In the optical absorption spectra of the Au/TiO₂ film, the localized surface plasmon resonance (LSPR) peak of Au nanoparticles was observed at 534.5 nm. When the film was immersed in various kinds of solutions, such as alcohols, NaCl and d-glucose aqueous solutions, a linear relation was clearly observed between the LSPR peak wavelength and the refractive index of the solutions, in the range of 1.0003–1.4181.     

Solvothermal synthesis and photoluminescence properties of ZnO nanorods and nanorod assemblies from ZnO2 nanoparticles

Without the use of any extra surfactant or template, hexagonal phase ZnO crystallites consisting of individual nanorods or nanorod assemblies were synthesized simply by solvothermal treatment of several nanometer ZnO₂ nanoparticles in three different solvents (including ethanol, 80 wt.% hydrazine hydrate aqueous solution and ethylenediamine) at 150 °C for 24 h. The structures and optical properties of the resultant products were characterized by means of X-ray powder diffraction (XRD), scanning electron microscope (SEM), and room temperature photoluminescence (RTPL) spectra. The RTPL spectra of the resultant products all showed a much stronger ultraviolet bandgap emission peaking at around 387 nm and a weaker emission associated with the defect level. The as-synthesized ZnO crystallites are promising materials for the optoelectronic devices due to their excellent UV emission properties.     

Fabrication of thermochromic composite using monodispersed VO2 coated SiO2 nanoparticles prepared by modified chemical solution deposition

Monodispersed thermochromic VO₂ particles were fabricated by VO₂ coating onto monodispersed SiO₂ nanoparticles with the modified chemical solution deposition technique using vanadium isopropoxide solution and monodispersed SiO₂ particle suspension solution. The average size of the resultant VO₂–SiO₂ particle was 57 nm and the coating thickness of the VO₂ layer was 6 nm. A thermochromic composite was fabricated using the VO₂–SiO₂ particles and a poly lactose acid polymer as a transparent matrix, and the transmittance of the composite at a high temperature was 10% less than that at a low temperature.     

Microstructures of YBa2Cu3O7/La0.7Ca0.3MnO3 and La0.7Ca0.3MnO3/YBa2Cu3O7 bi-layers grown on (001)LaAlO3

Epitaxial YBa₂Cu₃O₇/La_0.7Ca_0.3MnO₃ (YBCO/LCMO) bi-layers and La_0.7Ca_0.3MnO₃/YBa₂Cu₃O₇ (LCMO/YBCO) bi-layers were grown on (001)LaAlO₃ by pulsed laser deposition, and their microstructures were compared by transmission electron microscopy investigation. In the YBCO(100 nm)/LCMO(150 nm) bi-layers, the LCMO layer consists of columnar grains of ~ 17 nm in diameter and contains mixed orientation domains of [100]_c, [010]_c and [001]_c. The YBCO layer is totally c-axis oriented and the YBCO lattices are tilted − 2.5° to + 2.5° as they grew on the rough surfaces of LCMO columnar grains. For the LCMO(140 nm)/YBCO(140 nm) bi-layers, the LCMO/YBCO interface is sharp and flat. The initial 12-nm thickness of the YBCO layer is composed of c-axis oriented domains, and the upper part of YBCO layer is [100] oriented. The LCMO layer was predominantly [001]_c oriented while [100]_c-oriented domains were occasionally observed.     

Solvothermal preparation of Bi2WO6 nanocrystals with improved visible light photocatalytic activity

Bismuth tungstate (Bi₂WO₆) nanocrystals with the average size of ca. 12 nm had been successfully synthesized by a simple solvothermal method at 180 °C for 2 h. The as-synthesized Bi₂WO₆ nanocrystals were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, UV–vis diffuse reflectance spectra, and N₂ adsorption–desorption measurements. The visible-light-driven photocatalytic activity of the sample was evaluated by photo-degradation of rhodamine-B (RhB) at room temperature, which is much higher than that of the hydrothermal synthesized Bi₂WO₆ square plates and the commercially available TiO₂ (P-25). We believed that the high photocatalytic activity could be ascribed to the intrinsically small grain size and high surface-to-volume ratio associated with the Bi₂WO₆ nanocrystals.     

Superior bactericidal activity of SDS capped silver nanoparticles: Synthesis and characterization

Silver nanoparticles were synthesized through UV photo-reduction of silver nitrate aqueous solution, containing ethanol and sodium dodecyl sulfate (SDS) using an UV digester equipped with high pressure mercury lamp of 500 W. The synthesized nanoparticles were characterized by UV–vis spectroscopy (UV–vis), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). The formation of silver nanoparticles was confirmed from the appearance of surface plasmon absorption maxima at 418 nm. TEM showed the spherical nanoparticles with size in 23–67 nm (average 45 ± 10 nm). The silver nanoparticles were stable for more than 8 months. The antibacterial activity of these SDS capped silver nanoparticles was tested using Pseudomonas aeruginosa as a model strain for gram-negative bacteria. SDS capped silver nanoparticles exhibit a much higher bactericidal activity compared to silver nanoparticles capped with other capping agents. Even at a low silver nanoparticle concentration of 5 μg/ml, complete inhibition of 10⁷ colony forming units (CFU) was achieved with SDS capped silver nanoparticles. This concentration is much lower than the values reported by other authors. This enhanced bactericidal activity is attributed to much efficient transport of silver nanoparticles by SDS to the outer membrane of cell wall compared to the other capping agents and have a better interaction of nanoparticles with the cell.     

Photoluminescent characterization of KNbO3:Eu

In this study, the photoluminescence (PL) spectra of europium-doped potassium niobate (KNbO₃) crystallites prepared by a vibrating milled solid-state reaction method were studied. X-ray diffraction (XRD), scanning electron microscopy (SEM) and optical spectral analysis (luminescence excitation, emission spectra and time-resolved spectra) were used to characterize the KNbO₃:Eu³⁺ powders. The results of the XRD revealed that the powders remained as a single orthorhombic structure at doping concentrations below 3 mol%. A second phase of EuNbO₄ begins to appear at 5 mol%. The ⁵D₀–⁷F₁ (593 nm) and ⁵D₀–⁷F₂ (614 nm) emission characteristics of Eu³⁺ appear at a quenching concentration of above 3 mol%. The Commission Internationale d’Eclairage (CIE) chromaticity coordinates of a Eu:KNbO₃ host excited at λ_ex = 400 nm and λ_ex = 466 nm wavelengths, both presented a red-shift when increasing the Eu³⁺ ion doping. The lifetime of the Eu³⁺ ion decreased as the doping concentration was increased from 1 to 7 mol%.